functions.php adding item to end of menu. I want to change position

Using PHP operators you can change:

$items .= '<li class="register"><a href="' . $registration_topmenu_url . '" class="section-button">' . stripslashes($reg_widget['registrationtopmenutext']) . '</a></li>';

To

$rbutton = '<li class="register"><a href="' . $registration_topmenu_url . '" class="section-button">' . stripslashes($reg_widget['registrationtopmenutext']) . '</a></li>';
$items = $rbutton . $items;